This invention relates generally to a force transmitting apparatus and more specifically to a force transmitting apparatus which is advantageously utilized to effect turning movement of a steerable wheel of a vehicle.
A known variable ratio steering apparatus is disclosed in U.S. patent application Ser. No. 868,114 filed Jan. 9, 1978 by Frederick John Adams and Ralph Malcolm Lehman and entitled "Rack And Pinion Assemblies". The steering apparatus disclosed in that application includes a pinion having teeth which mesh with helical gear teeth on a rack bar. The rack bar is displaced longitudinally relative to a housing upon rotation of the pinion. A cam track is disposed on the rack bar and is engaged by a follower which is connected with the housing. The cam track and follower cooperate to effect rotation of the rack bar upon longitudinal movement of the rack bar. This rotation of the rack bar causes the rack gear teeth and pinion gear teeth to interact in such a manner as to vary the rate of axial movement of the rack bar.
Although the steering apparatus disclosed in the aforementioned application is believed to be generally satisfactory in its construction and mode of operation, it is believed that after extended usage, ball joints at opposite ends of the rack bar may tend to wear. This wear of the ball joints is, to some extent at the least, induced by the rotation of the rack bar.
In addition, the cam track of the steering apparatus disclosed in the aforementioned application is axially offset from the rack gear teeth. Therefore, the rack bar must have a minimum length which is at least twice as great as the length of the array of rack gear teeth. It is believed that this relatively long length may be objectionable if the steering apparatus is used with relatively small vehicles. In addition, by having the cam track axially offset from the rack gear teeth, the rack gear is subjected to both torsional and bending forces when the rack gear is rotated by the cam follower.